The processing of semiconductor substrates is integral to the manufacture of integrated circuits. Most commonly, these substrates are in the form of silicon wafers that are five to eight inches in diameter, although a variety of other substrates of various sizes are also known. A single wafer can be exposed to a number of sequential processing steps including, but not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), etching, planarization, and ion implantation.
The use of robots has become standard in semiconductor processing. Robots can process a large number of substrates through many different processing technologies, and can perform repetitive tasks quickly and accurately. The use of robots thus eliminates human fatigue and minimizes operator errors as factors in the fabrication process.
Most modern semiconductor processing systems include robotic cluster tools that integrate a number of process chambers together in order to perform several sequential processing steps without removing the substrate from the highly controlled processing environment. These chambers may include, for example, degas chambers, substrate preconditioning chambers, cooldown chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers, and etch chambers. The combination of chambers in a cluster tool, as well as the operating conditions and parameters under which those chambers are run, are selected to fabricate specific structures using a specific process recipe and process flow.
Once the cluster tool has been set up with a desired set of chambers and auxiliary equipment for performing certain process steps, the cluster tool will typically process a large number of substrates by continuously passing them, one by one, through the chambers or process steps. The process recipes and sequences will typically be programmed into a microprocessor controller that will direct, control and monitor the processing of each substrate through the cluster tool. Once an entire cassette of wafers has been successfully processed through the cluster tool, the cassette may be passed to yet another cluster tool or stand alone tool, such as a chemical mechanical polisher, for further processing.
One example of a fabrication system of the type described above is the cluster tool disclosed in U.S. Pat. No. 6,222,337 (Kroeker et al.), and reproduced in FIGS. 1-4 herein. The magnetically coupled robot disclosed therein is equipped with robotic arms having a frog-leg construction that are adapted to provide both radial and rotational movement of the robot blade within a fixed plane. The radial and rotational movements can be coordinated or combined to allow for pickup, transfer and deliver of substrates from one location within the cluster tool to another location. For example, the robotic arm may be used to move substrates from one processing chamber to an adjacent processing chamber.
With reference to FIG. 1, which is a schematic diagram of the integrated cluster tool 10 of Kroeker et al., substrates are introduced into, and withdrawn from, the cluster tool 10 through a cassette loadlock 12. A robot 14 having a blade 17 is located within the cluster tool 10 to transfer the substrates from one process chamber to another. These process chambers include the aforementioned cassette loadlock 12, a degas wafer orientation chamber 20, a preclean chamber 24, a PVD TiN chamber 22 and a cooldown chamber 26. The robot blade 17 is illustrated in the retracted position in which it can rotate freely within the chamber 18.
A second robot 28 is located in transfer chamber 30 and is adapted to transfer substrates between various chambers, including a cooldown chamber 26, a preclean chamber 24, a CVD Al chamber (not shown) and a PVD AlCu processing chamber (not shown). The specific configuration of chambers illustrated in FIG. 1 is designed to provide an integrated processing system capable of both CVD and PVD processes in a single cluster tool. A microprocessor controller 29 is provided to control the fabricating process sequence, conditions within the cluster tool, and the operation of the robots 14, 28.
FIG. 2 is a schematic view of the magnetically coupled robot of FIG. 1 shown in both the retracted and extended positions. The robot 14 (see FIG. 1) includes a first strut 81 rigidly attached to a first magnet clamp 80 and a second strut 82 rigidly attached to a second magnet clamp 80′. A third strut 83 is attached by a pivot 84 to strut 81 and by a pivot 85 to a wafer blade 86. A fourth strut 87 is attached by a pivot 88 to strut 82 and by a pivot 89 to wafer blade 86. The structure of struts 81-83, 87 and pivots 84, 85, 88, and 89 form a “frog leg” type connection of wafer blade 86 to magnet clamps 80,80′.
When magnet clamps 80,80′ rotate in the same direction with the same angular velocity, then the robot also rotates about axis x in this same direction with the same velocity. When magnet clamps 80, 80′ rotate in opposite directions with the same absolute angular velocity, then there is no rotation of assembly 14, but instead there is linear radial movement of wafer blade 86 to a position illustrated by dashed elements 81′-89′.
With reference to FIGS. 3 and 4, a wafer 35 is shown being loaded on wafer blade 86 to illustrate that the wafer blade can be extended through a wafer transfer slot 810 in a wall 811 of a chamber 32 to transfer such a wafer into or out of the chamber 32. The mode in which both magnet clamps 80, 80′ rotate in the same direction at the same speed can be used to rotate the robot from a position suitable for wafer exchange with one of the adjacent chambers 12, 20, 22, 24, 26 (see FIG. 1) to a position suitable for wafer exchange with another of these chambers. The mode in which both magnet clamps 80, 80′ rotate with the same speed in opposite directions is then used to extend the wafer blade into one of these chambers and then extract it from that chamber. Some other combination of clamp rotation can be used to extend or retract the wafer blade as the robot is being rotated about axis x.
To keep wafer blade 86 directed radially away from the rotation axes x, an interlocking mechanism is used between the pivots or cams 85, 89 to assure an equal and opposite angular rotation of each pivot. The interlocking mechanism may take on many designs. One possible interlocking mechanism is a pair of intermeshed gears 92 and 93 formed on the pivots 85 and 89. These gears are loosely meshed. To eliminate play between these two gears because of this loose mesh, a weak spring 94 (see FIG. 4) may be extended between a point 95 on one gear to a point 96 on the other gear such that the spring tension lightly rotates these two gears in opposite directions until light contact between these gears is produced.
The use in semiconductor processing of robots of the type depicted in U.S. Pat. No. 6,222,337 (Kroeker et al.) has several advantages, some of which have already been noted. In particular, such robots can improve the speed and accuracy of the manufacturing process. Moreover, the use of robots offers the potential for reducing or eliminating contamination of semiconductor substrates, which is a well known problem attendant to the human handling of such substrates. This consideration is becoming increasingly important as the trend to further reduce the dimensions of integrated circuits continues, since the presence of impurities becomes more damaging and these dimensions are reduced.
Unfortunately, while the use of robots in semiconductor fabrication processes offers many advantages, it also posses some challenges of its own. For example, many robots used in semiconductor processing, including those of the type depicted in U.S. Pat. No. 6,222,337 (Kroeker et al), have wrist assemblies that have been found to exhibit excessive yaw during use. This can result in a number of complications, such as undesirable contact between the robot and the cassette loadlock, which in turn can result in maintenance issues and product contamination. This problem is exacerbated at higher assembly speeds, due to the increased momenta involved. Unfortunately, fabrication plants are being required to operate at ever increasing speeds, due to the need for greater product throughput and efficiency. Hence, excessive yaw is a problem that must be reckoned with. Excessive yaw also causes inaccuracies in the positioning of the wafer. These inaccuracies can result in process failures that may culminate in loss of the wafer. Excessive yaw also accelerates wear in processing equipment due to tooth-to-tooth collisions between gear elements.
Some wrist assemblies have been developed with the goal of addressing the aforementioned problems. One such assembly is shown in FIG. 5. The wrist assembly 201 shown therein comprises first 213 and second 215 arms. The first and second arms terminate, respectively, in first 217 and second 219 radii which rotatingly engage first 221 and second 223 pivots attached to a blade mount 225 by a series of fasteners 227. A blade (not shown) can be secured to the blade mount via machine screws 229.
FIGS. 6 and 7 illustrate the means by which the first 217 and second 219 radii rotatingly engage the first 221 and second 223 pivots. First 231 and second 233 steel bands are provided that wrap around a portion of the radius of each of the first 217 and second 219 radii. The first band 231 is secured to the first radius 217 by means of a first tension plate 241, and is secured to the second radius 219 by means of a first terminus 253. Similarly, the second band 233 is secured to the second radius 219 by means of a second tension plate 243, and is secured to the first radius 217 by means of a second terminus 251.
The first tension plate 241 is shown in greater detail in FIG. 6. As seen therein, the first band 231 is adjoined to the first tension plate 241 by way of a first weld joint 261. The first tension plate 241 is secured to the second radius 219 by means of a spring-loaded screw 271.
The first terminus 251 is shown in greater detail in FIG. 7. As seen therein, the first band 231 is adjoined to the first terminus 251 by way of a second weld joint 263. The first terminus 251 is, in turn, secured to the first radius 217 by way of a screw 273.
The band configuration described above is advantageous in that it effectively interlocks the movement of the first 213 and second 215 arms. Such a configuration is especially useful in semiconductor processing equipment having a frog leg design because, when properly implemented, it can essentially eliminate yaw.
Unfortunately, the aforementioned wrist assembly design has been found to require considerable maintenance in the field. For example, the first and second bands 231, 233 are prone to fracturing, thus requiring down time in the assembly line while new bands are installed. Given the extreme cost of downtime in semiconductor manufacturing, there is a need in the art to create a more robust design for a wrist assembly that overcomes this problem. There is also a need in the art for robotic arm assemblies which are suitable for use in semiconductor fabrication, which exhibit minimal yaw, and which can be used to accurately position wafers in a fabrication line. There is further a need in the art for a wrist assembly design that has no collision points, and thus exhibits a longer life cycle and reduced wear. These and other needs are met by the devices and methodologies disclosed herein and hereinafter described.